This type of D.C. power supply is used, in particular in telecommunications, for integrated service digital networks where the digital terminals that give users access to a wide range of telecommunications services consume too much power to be capable of being remotely powered from the local switching exchange like conventional telephone sets, but where it is nevertheless essential to ensure a minimum telephone service in the event of a failure in the mains locally powering a digital terminal.
The object of the present invention is to provide emergency D.C. power supply of the above-mentioned type where two power sources are capable of operating naturally even when they are geographically separate, without requiring a special signalling link between the sources, thereby making it possible to integrate such an emergency power supply into an access point to a digital network without it being necessary to provide special cabling for a signalling link between the two power sources.